(
    function() {
        function bindEvent() {
            document.onclick = handlerClick;
        }

        function handlerClick() {
            alert("hello gulp");
        }
        bindEvent();

        class Foo {
            constructor() {
                this.a = 10;
            }
        }
        let f = new Foo();
        let arr = Array.from({ a: 10 });
    }
)()